Apparatus for railway signal systems



Sept. 24, 1946.

F.T.FEREDAY APPARATUS FOR RAILWAY SIGNAL SYSTEMS- s Sheets-Sheet 1- Filed Jan. 6, 1944 INVENTOR haw Hi1 ATTORNEY Sept. 24, 1946. T, FEREDAY 2,408,206

APPARATUS FOR RAILWAY' SIGNAL SYSTEMS Filed Jan. 6, 1944 s Sheets-heet 2 INVENTOR H11 ATTORNEY fipdepia ZVZweday- Sept. 24, 1946.

F. T. FEREDAY APPARATUS FOR RAILWAY SIGNAL SYSTEMS Filed Jim. 6, 1944 s Sheets-Sheet 3 BYa . m1 AT-TORNEY direct current wherewith only Patented Sept. 24, 1946 APPARATUS FOR RAILWAY SIGNAL SYSTEMS Frederick T. Fereday, Louisville, Ky.,.assignor to The Union Switch and Signal Company,.Swissvale, Pa., a corporation of Pennsylvania Application January 6, 1944, Serial No. 517,197

My invention relates to apparatus for railway signal systems, and more particularly to apparatus for such systems using coded track circuit energy.

Railway signal systems using coded direct cur rent track circuits are not dependent upon a transmission line which is subject to broken line wiresv caused by weather and other conditions. Heretofore the arrangement for coded direct current track circuits has been to use two sources of current, a relatively large or 12 volt battery for operating the code transmitters and a single cell or low voltage battery for the track circuit. Such two battery'arrangement adds to thecost and maintenance. Also there is a certain loss 'of energy in the current limiting resistor usually interposed in the connection between the track battery and the rails. f

Accordingly, a feature of my invention is the provision of railway signalsystems incorporating novel and improved track circuit coding apparatus.

Another feature of my invention is the provision of apparatus for track circuits using coded a single battery is required.

Again, a feature of my invention is the provision of track circuit apparatus of the type here involved wherewith the code transmitter is connected in series with the track battery taking the place of the usual current limitingresistor and the energy usually consumed in such resistor is utilized for operation of the code transmitter.

Still another feature of my invention is the provision of railway signal apparatus incorporating novel approach control means to cooperate with coding track circuit apparatus to effect an approach control for two sections in advance of a train.

,Other features, objects and advantages embodyingmy invention will appear as the specification progresses. S

The features, objects and advantages embodying my invention are accomplished by providing a low voltage code transmitter that is operable from the usual low voltage track battery, and ap proach control apparatus of the feed-back code principle arranged to cooperate with such trans- ;mitter. This code transmitter is made to operate on the. energy usually consumed in the current limiting resistor interposed between the track battery and the track rails and it is connected in series with the track battery through a contact ;on;a first armature of the transmitter causing ,such first armature to oscillate. Thetransmitter- 2 Claims. (01. 246-38 predetermined frequency of oscillation, and thus the track circuit current is periodically interrupted at a rate corresponding tothe oscillating frequency predetermined for the code transmitter. Preferably, the code transmitter is. constructedwith a second armature which isbiased so that this second armature is operated only when the energizing current flowing in the-winding of the transmitter is-of a relatively high value. Thissecond armature is adjusted to remain-at its biased position with the respective track circuit unoccupied and to be attracted to a picked-up position when a train enters the section to shunt the rails and the track circuit current is increased. This second armature is used to provide an approach control. As an alternative, the second armature of the'transmitter canbe replaced by a relay, the winding of which is connected. in series with the code transmitter winding in the track battery connection, and this relay is adjusted to be picked up only when the track circuit current is increased due to a train occupying the section.

The approach control apparatus also includes means governed by the code following track relay to supply feed-back current impulses to the track rails during each off code period of the track circuit current and an approach relay connected to the rails through a contact carried on the first armature of the code transmitter. This last mentioned contact is closed as the first armature-is moved to its attracted position, and the approach relay is connected across the rails each oil code period of the track circuit current to receive the feed-back currentimpulse supplied to the rails at the relay end of the track circuit. As an alternative, this approach relay may be connected across the'rails through a, rectifier disposed to pass the feed-back impulses, but block the flow of current from the usual track battery. This approach control relay and the second armature of the code transmitter provide two approach control conditions, one of which becomes effective when a train enters the section next in the rear of the associated section, and the second of which condition becomes effective when the train enters the associated section.

If more than two different control conditions of the coded track circuit current are required, the traffic controlled circuits are arranged to Pole change the connection of the track battery, the code transmitter being operable with equal efiiciency by current of either polarity. In this w y the track circuit current is coded at a preselected code rate, and is of either positive or negative polarity according to traffic conditions. When the track circuit is polarized, a polarized code following track relay is provided. Again, more than two different control conditions may be provided by using code transmitters of different predetermined operation frequencies and arranging the trafiic controlled circuits to selectively connect these transmitters into the track circuit according to difierent traffic conditions.

I shall describe three forms of apparatus embodying my invention, and shall then point out the novel features thereof in claims.

In the accompanying drawings, Figs. 1 and 2 are diagrammatic views showingia first and a second form of apparatus, respectively, embodying my invention when used with polarized track circuits. Fig. 3 is a diagrammatic view showing a form of apparatus embodying my invention for track circuits using currents of different code rates. g

In each of the three views like reference characters are used to designate similar'parts.

Referring to Fig. 1, the reference characters 1a and lb designate the rails of a stretch of railway over which trafiic normally moves in the direction indicated by an arrow, and which rails are formed by insulated rail joints with consecutive track sections of a signal system, and of which sections only the one section D--E and the adjoining ends of the two adjacent sections are shown, because these are sufficient to illustrate the principle of my invention.

Each track section is provided with coded track circuit apparatus, control relays, wayside si nals and approach control apparatus.

The type of wayside signal to be used is immaterial, and signals SD and SE for section DE and the section next in advance of section D-E are of the color light type capable of displaying a red lamp R, a yellow lamp Y and a green lamp G, for stop, approach and clear signal indications, respectively.

The track circuit apparatus for each section includes supply means connected across the rails at the exit end of the section and code following relay means connected across the rails at the entrance end of the section. Thus at the junction of adjacent sections, such as location E, for example, there are placed the code following relay means for the track circuit of the section immediately in advance and the supply means for the track circuit of the section immediately in the rear.

The supply means for the track circuit of section DE includes a track battery BE and a code transmitter CT. The battery BE is preferably of the split battery type having a positive terminal B3, a negative terminal N3 and a mid terminal C. Thus this battery is capable of supplying current of either polarity at the low voltage used for track circuits.

The code transmitter CT may take different forms, and preferably it is of the relay type. Transmitter CT is provided with a first armature or contact member 4 and a second armature or contact member 5. The first armature A is biased by weight, or otherwise, to a first position where it engages a contact 6 and is attracted to a second position where it swings out of engagement with contact 6 and into engagement with a contact 1 when a winding 8 of the transmitter is energized. With winding 8 energized through contact 4-6, the armature 4 oscillates between its two positions at a frequency predetermined by the weight and construction of the parts. By way of illustration to aid in understanding my invention, I shall assume that transmitter CT is constructed for armature 4 to have an operation frequency of 15 times per minute, it being in engagement with each contact 6 and l for substantially one-half of each operation cycle. The second armature 5 is spring or otherwise biased to a released position and is attracted against the force of its bias to a picked-up position when the transmitter is energized at a relatively high preselected energy level. That is, when code transmitter CT is supplied with current of a relatively low value but suflicient for proper operation of the first armature 4, the second armature 5 is retained at its released position by that when current of a relatively high value flows in winding 8, armature 5 is picked up to engage a front contact 9, the armature 4 being operated at its predetermined frequency by such increased current.

Code transmitter CT is energized by track battery BE, winding 8 and contact 4-6 being interposed in series in the connection of track battery BE to the rails of the section D-E. To be explicit, a circuit can be traced from positive terminal B3 of battery BE, either through front contact I!) of a relay ED to be referred to later, or through front contact II of a relay EH, also to be referred to later, and back contact l2 of relay ED, wire l3, thence through winding 8 and contact 46 of the transmitter, wire I4 to rail lb, through the track relay of the associated track section, to be described hereinafter, or

through a train shunt if a train occupies the section, track rail la, and wire 15 to the center terminal C of battery BE. Again, a circuit can be traced from the negative terminal N3 of battery BE through back contacts l6 and I2 of relays EI-I and ED, respectively, wire I3 and thence as previously traced to the center or mid terminal C of the battery. Thus, when relay ED is picked up to close front contact II], or relay EH is picked up to close front contact H, and relay EDis released to close back contact l2, the track battery BE is connected to the rails of the section D-E through the code transmitter and the track circuit is supplied with coded current of what I shall'call positive polarity. When both relays EH-and ED are released, the track circuit current is coded and it is of what I shall call negative polarity. If the track section D-E is unoccupied, the value of the track circuit current is of a normal or relatively low value, and the second armature 5 of the code transmitter remains at its released position. If a train occupies the section the track circuit current is increased and the second armature 5 is picked up to close front contact 9.

The code following track relay means for the track circuit of section DE may be any one of several different arrangements of the polarized type. In Fig. 1, two code following neutral relays DR! and DR2 are connected in multiple to the rails through rectifiers I l and I8, respectively, the arrangement being such that relays DRI and D'RZ are operated by current of positive and negative polarity, respectively. The connection of relay DRI can be traced from rail lb through wire i9, rectifier IT in its forward direction, winding of relay DRI, wire 20, back contact 2| of a relay DH to be referred to shortly, and wires 22 and 23 to rail la. The connection for relay DB2 extends from rail la through wire 23, rectifier [8 in its forward direction, winding of relay DR2,.

wire 24, back contact 25 of a relay DD to be referred to shortly, and wires 26 and I9 to rail lb. It follows that relay DRI' is code operated when coded track circuit current of positive polarity is'supplied to the track circuit in the manner explained hereinbefore, and relay DR2 is operated by track circuit current of negative polarity.

It is to be pointed out that code following track lays'DRl and DB2, and these controlrelays goV- em in turn the signal SD and the track circuit for the section next in the rear of section DE. Similarly, control relays ED and EH at location E are governed by the track relays ERI and ERZ and these control relays govern in turn the signal SE and the track circuit for section DE,

Looking at location E, relay EH is governed by relay ER2 through a condenser 21, which functions as a secondary source of energy. When relay ERZ is picked up, the condenser 21 is connected to a charging circuit which includes a battery the terminals of which are designated Bill and NH), and which charging circuit. extends from terminal BIO through front contact 28 of relay ER2, condenser 21, wire 29, and to terminal N l 0 through three alternative paths which include front contacts 30, 3| and 32 of relays AP, FTP and APP, respectively, and which relays are a part of the approach control apparatus to be described hereinafter. Then, when relay ERZ is released to close back contact 33, the condenser 27 is connected across a winding of relay EH and relay EH is energized due to the discharge of the condenser. Consequently, when relay ER2 is operated at a code rate, the control relay EH receives an energizin impulse each code cycle, and it is retained picked up from one code cycle to the next by virtue of a slow release period provided for the relay due to a rectifier 34 connect ed across its winding. Such energization of relay'EH is effected, however,yonly if one of the approach relays AP, FTP or APP is picked up to close the respective front contact 30, 3| or 32. In a similarmanner, the track relay ER! controls relay ED.. Relay ER! when picked up completes a charging circuit for a condenser 36, such circuit extending from terminal BIO through front contact35 of relay ERI, condenser 36, wire :29 and to terminal NIB by the three alternative circuit paths explained in connection with the 'next. Control relays ED and EH govern the connection of battery BE to the track circuit for section DE as explained hereinbefore, and also govern operating circuits for the associated signal SE in a manner to be explained when the operation of the apparatus is described.

inspection of the drawings taken in connection with the description ofthe control of relays EH' pulse includes a condenser 39 and a current source. With either relay DRZ picked up to close front contact 40, or relay DRI picked up to close front contact 4|, condenser 39 is charged by a circuit connected to a battery which may be track battery BD at location D, or a separate battery. This charging circuit extends from terminal B3 of the associated battery through either front contact 40 or 4|, condenser 39 and to terminal N3 ofthe same source of current, through a connection, not shown, but which circuit connection would be similar to the connection of a condenser 42 at location E, and which latter condenser supplies the feed-back current impulse for the track circuit for the section next in advance of section DE, and which connection for condenser 42 includes back contact 43 of relay AP and either front contact 44 of relay FTP or front contact 45 of relay APP. Condenser 39 is connected across the rails of'the section DE through alternative circuit, paths, one of which extends from one terminal of the condenser through back contact 46 of relay DRZ, front contact 41 of relay DH and, wires 26 and l9 to rail lb; and from the other terminal of the condenser through front contact 49 of relay DH'a-nd Wires22 and 23 to rail la. The other circuit path extends from one terminal of condenser 39 through back contact 59 of relay DRI, front contact 5| of relay DD and wires 22 and 23 to rail la; and from the other terminal of the condenser throughfront contact -52 of relay DD and wires 26 and I9 to rail lb. Consequently, when track relay DRZ is operated at code and the approach control relays for the section next in the rear are conditioned so as to complete the connection of the charging circuit for condenser 39 to'the terminal N3 of the associated battery, the condenser 39 is charged each on code period, and is connected across the rails to discharge and provide a feed-back code impulse each off code period. It is to be observed that this feed-back current impulse is of a polarity reverse to that of the track circuit current that operates the track relay DRZ. In like manner, code operation of track relay DRI connects condenseri39 to a charging circuit each on code period and connects the condenser across the rails each ofi code period to supply a feedback current impulse due to the discharge of the condenser, the feed-back current impulse being of a polarity reverse to the polarity of the track circuit current that operates track relay DRI.

Approach relay AR is connected across the rails through second position contact 1 of armature 4 of the code transmitter CT and thus relay AR is conditioned to receive the feed-back cur- 7 rent impulse supplied to the rails throughcon- Control relays DH and DD at location D are controlled by track relays DR! and DRZ through condensers 51 and 18 as will be apparent by an nected across its Winding,

Repeater relay APP isprovided with an obvious pick-up circuit including front contact 54 of re-' lay AP, and with a stick circuit which includes its own front contact 55 and back contact '6 of relay FTP. Relay FTP is energized through an obvious circuit including contact 59 of code transmitter CT.

Each of the remaining track sections or the signal system of Fig. 1 is provided with apparatus substantially the same as that described for section DE.

In describing the operation of the apparatus of Fig. 1, I shall assume that section DE, as well as the section next in the rear and the section next in advance are unoccupied. Under this trafilc condition, code operation of either track relay ER! or ER2 is ineffective to bring about the energization of the respective control relays ED and EH because the charging circuits for the associated condensers 35 and 21 are held open at front contacts 39, 3! and 32 of the approach conrol relays AP, APP and FTP of section DE. With control relays EH and ED deenergized, track battery BE is connected to the rails of section D--E for the track circuit to be supplied with coded current of negative polarity, and which coded current operates the track relay DRZ at location D. Operation of relay DB2 at this time is ineffective to govern the associated control rela DI-l, because the charging circuit for condenser 51 through which relay DH is controlled is not completed at the associated approach control relays in the same way the charging circuit of condenser 21 at location E is not completed through the contacts of the associated approach control relays of section DE,

No feed-back current impulse is provided for the section next in advance because the charging circuit for condenser 42 is normally open at front contacts 44 and 45 of the approach control relays FTP and APP, respectively, Likewise, no feed-back current impulse is supplied to section DE because the charging circuit for condenser 39 is open at the contacts of the approach control relays for the section next in the rear in the same manner that the connection of condenser 42 at location E is normally open at the approach control relays APP and FTP. Consequently, under normal conditions, all control relays and approach control relays are deenergized and all wayside signals are dark.

It is to be observed that in place of each track circuit being normally supplied with coded current of negative polarity, as illustrated in Fig. 1, the polarity of the track circuit current may be reversed for alternate track sections to aid broken down insulated rail joint protection.

I shall next assume that a train enters the section next in the rear of section DE. The shunting of the rails of the section next in the rear increases the flow of track circuit current for that section, and the second armature of the associated code transmitter is picked up to close its front contact, and which contact corresponds to contact 9 of transmitter CT. This causes the approach relay for the section next in the rear, and which relay corresponds to approach relay FTP, to be picked up through the second armaoff code period which causes in turn approach relay AR at location E to be operated and the associated repeater relays AP and APP to be energized.

The closing of front contact 3!] of relay AP completes the circuit by which condenser 21 is charged, and consequently the control relay EH is energized in response to code operation of track relay ER2. Relay EH on picking up to close front contact I I switches the connection of track battery BE and the track circuit of section DE is supplied with coded current of positive polarity causing track relay DRI to be operated in place of track relay DRZ; With relay DR] operated, the associated control relay DD is energized because condenser 18 is now changed each on code period due to the contact corresponding to contact 3| of relay FTP being closed at the corresponding relay for the section next in the rear. Relay DD on picking up to close front contacts 5! and 52 completes the connection for the feedback impulse for section DE. Also, the picking up of relay DD to close front contact completes a circuit by which green lamp G of signal SD is illuminated, this circuit being com'- pleted through contacts of the approach control relays for the section next in the rear in a manner similar to the control circuit for lamp G of signal SE at location E and which latter circuit is completed at front contact 58 of relay FTP and back contact 6| of relay AP when a train has entered section DE. Consequently signal SD is approach lighted to display'a clear signal, and feed-back impulses are supplied to section DE.

It is to be noted that signal SE remains dark while the train occupies the sectio'n'next in the rear of section DE because the control circuits of signal SE are held open at front contact 58 of relay FTP and at back contact 6| of relay AP.

It is to be observed that if another train occupies the section next in advance of the section D-E at the time the first assumed train is tra versing the section next in the rear of section DE, the train in the section next in advance shunts relays ERI and ERZ and both control relays EH and ED are deenergized causing the track circuit current for section DE to be of negative polarity so that track relay DRZ at location D is operated and control relay DH is energized in response to the charging and discharging of condenser 57. With control relay DH picked up the feed-back impulses are supplied as before, and with front contact 63 closed and relay DD releasedto close back contact 62,-

the yellow lamp Y of signal SD is illuminated for the signal to display an approach indication.

I shall next assume that the first mentioned train advances and enters section DE, the section next in advance being considered as unoccupied. The shunting of the rails of section DE shunts the track circuit current from the relays DR! and DR? and also the feed-back current impulse from relay AR. The shunting of both track relays DR! and DR2 causes both control relays DD and DH to be deenergized with the result the R lamp of signal SD is illuminated through a circuit including back contacts 52 and E05 of relays DD and DH. The shunting of approach relay AR causes this relay to be released and the repeater relay AP is deenergized and released at the end of its slow release period. The shunting of the rails of section DE causes an increase in the track circuit current so that armature 5 of the code transmitter CT is picked 9. up tobrin'g about the" energizing of approa'ch relay FrP; f'I-he pickin'gi'up of 'relay FTP opens ba'cl icontact 56 in the stick circuit for relay APP and thatrelay' is deenergiz'ed subsequent to. the rele'aseof relay AP. With relay AP "released to fclose back contact 43 and relay FTP picked up to? close front contact 44, the charging. cireuit'ror: condenser 42 is completed and feed-back currentimpulses are no-W supplied to the rails ior 'thesection next in advance to govern the approach relay at -the;-eXit '*end ofthe section, and which approach relaycorresponds to relay Release .of relay 'APLto'close back contact 61 and the picking up of relay FTP to close front contact 58 completes-the operating circuit to illuminate either the green lamp'G or the yellow I lamp-Y ofsignal SE according to which contr'ol relay ED or EH is picked up in. response to traffic -conditions in advance of section DE. Ifase'cond train occupie'sthe section in'advance to bring about the release of both control relays andED, closing back contacts 64 and 65, the 'red'lamp R of signal'SE is illuminated as a stop signal indication.

-In the'case the increaseoftrack circuit current when .thetrain firstenterssection DE is not sufficient to pick up the second armature 5' of code transmitter CT and the current'does not reach the value at which the second armature is' picked up untilthetrain has advanced some distance into section DE, the relay APP is retained'picked up by its stick circuit and the operating ci-r cuit for signal SE is completedat front contactfifi of relay APP. Also the charging circuits forcondensers 21 and 36 are completed at frbntaconta'ct .32 of relay APP, and the charging circuit for the condenser 42 is completed at 'front contact" 45 of relay APP'until' suchtime as the armature 5 of the code transmitter is-operated to bring about the energization of relay FTP.

When this train vacates section 'D--E shunting relays ER! and ERZ, both control relays ED and EH arerelea'sed so that the track circuit'fo'r section DE is again supplied with current offnegative polarity and the apparatus is restored to its normal condition. 1 In Fig.2, the" apparatus is the same as thatf-in Fig. 1, except for the means for s'up'plying' the to fully illustrate this form of apparatus embodyme my invention. In Fig.2 thefeed-back current'impulse is obtained from the track'battery or'preferably a separate battery of equivalent voltage, and a relay. Looking at location E of Fig. 2, and assuming that track relay ERZ i being operatedin response to coded track circuit current-for the section next in advance of section 'D- -E, a circuit for energizing a relay EF is formed each off code period, such circuit being traced from terminal B3'of the respective source of current, through back contacts 68 and .61 'ofrelays ER] andERZ, winding of relay EF, a rectifier-6B, :wire 10,back'co ntact.43 of relay AP and either front-contact; 44 of relay FTP or front contact 45 ot relay APP to terminal N3 of the samesource oncurrent. Relay'E F is providedwith a slow 'pick-up-period which is something less" than the on code period of the track circuit current." During this slow pick-up period of relay EF,-'- current nows from terminal B3 through back contacts 68-and 61,back contact H of relayEF, resistor relayfor the section next in advance and which approach relay corresponds to 'relay AR for section D'-E, track rail :Ia wire :15, front contact 1-6 of relay EH, Wires Tl andl'lfl, back contact 43 of relay 'AP and either front contact MS of relay'FTP or front contact 45 of relay APP to' terminal N3. "This feed-back current impulse thus supplied to the rails of'the section next in advance will operate the approach relay that corresponds-to-relay. AR and effect the approach control apparatus-for that section. ,If relayERl is'code operated the circuit for the feed-back impulse is completed at front contacts I04 and HIE-of relay ED} It is apparent that the apparatus of Fig. will operate in a manner similar to the apparatus of .Fig. 1 under the difierent trafiic conditions and a description of the' operation of the apparatus of Fig. 2 need not befur- 'ther described.

In Fig.--3,-inwhich a form of apparatus embodying my invention using different code rates is disclosed, the stretch of railway is arranged with track sections and wayside signals the same as in Fig. 1, and each section is provided with track circuit apparatus, signal control relays and approach control relays, the same as in Fig. 1.

The supply means for the track circuit of section D- E of Fig. 3 comprises a battery BEI and two code transmitters CT15- and CTIBU, The codetransmitters C'IJ5 and CTIBII are similar in construction to codetransmitter-CT of Fig. 1, transmitter 'CT'I5 being constructed to have an operation frequency bf '75 times per minute, and transmitter-CT! an operation frequency of times per minute. It will be understood; of course, that other operation frequencies may be selected forlthesecode transmitters. These'two transmitters are also adjusted for their respec- 'tive second armatures 19 and 80to be picked up at the same preselected'relatively high value of current that was provided for transmitter CT. Battery BEI is-connected to the rails of the associated section through one or the other of the transmitters} a first connection including front contact 8 I of control relay EH, winding-and contact 82 of transmitter CTI8U, track rail lb; track r'elay or train shunt and track rail Ia and wire 83 to the other'terminal of battery BEL A' second connectionincludes back contact 84 of conn01 relay"EH,' winding and contact $5 of transmitter'QT'IS and thence as previously traced for the first circuit connection. Thus when control relay EH is energized, the track circuit fortrack section D -E is supplied with coded current of "across the rails through a rectifier 86 which is poledto passcurrent of the polarity supplied by battery 'BEI, and'to block the feed-back current impulseused for control of theapproach control apparatus to be described shortly. At loca:

'tion E; track relay EH3 associated with the track section-next in advance is connected to the rails in-a manner similar to that oftrack relay DB3.

Track relay DB3 governs control relays DH and DD through a repeater relay TPD and a decoding unit IBUDU. Similarly, track relay ER3 governs associated control relays EH and ED through a" repeater relayTPE and a decoding funit FIBODU. "Looking at location E, track relay ER'3 when picked up to close front contact 88 11 completes an obvious circuit for energizing repeater relay TPE, and which circuit is completed through front contact 30, 3| or 32 of the relays AP, FTP or APP in the manner explained in connection with Fig. 1. It follows that when relay ER3 is operated at code, the repeater relay TPE is operated at a corresponding code providing the approach control relays are properly conditioned. With relay TPE picked up to close front contact 89, condenser 81 is charged through a circuit completed at front contact 30, 3! or 32, and condenser 81 is discharged through the winding of control relay EH when repeater relay TPE is released to close its back contact 90, during each off code period. With relay EH thus picked up in response to code operation of track relay EH3, the closing of front contact 9| of relay EH completes a circuit for supplying current impulses to the input side of the decoding unit IBDDU through front and back contacts 92 and 93 of repeater relay TPE. Decoding unit I8IJDU may be of any one of the several wellknown arrangements, and is shown conventionally for the sake of simplicity. It is suflicient to point out that when current impulses supplied to the input side of the unit are of the 180 code rate the control relay ED connected to the output side of the unit is energized and picked up, but that when the code impulses are of the 75 code rate, the control relay ED is deenergized and released. Control relays EH and ED, together with the approach control relays for section D-E govern the operating circuits for signal SE the same as in Fig. 1. Control relays DH and DD at location D are controlled by repeater relay TPD in a manner similar to that by which relays EH and ED are controlled by relay TPE.

The approach control apparatus of Fig. 3 is similar to that described for Fig. 1, and it is believed that this approach control apparatus of Fig. 3 can best be understood from a description of the operation of the apparatus. It is to be understood, of course, that location D of Fig. 3, and each similar location are provided with apparatus similar to that for location E of Fig. 3.

Normally, that is, when section DE and the adjacent sections of Fig. 3 are unoccupied, track relay EH3 is code operated, but control relay EH and in turn control relay ED remain deenergized because the circuits for the repeater relay 'I'PE and condenser 81 are not completed at contacts 39, 3| or 32 of the associated approach control relays. With relay EH released, closing back contact 84, the track circuit for section DE is of the '75 code rate, and track relay DB3 is operated at a corresponding code rate. Thus, in Fig. 3, all control relays and approachcontrol relays are normally deenergized and the signals are dark.

I. shall next assume that a train enters the section next in the rear of section DE. This causes the track circuit current for the section next in the rear to be increased, and the respective second armature of the code transmitter is picked up so that the relay corresponding to relay FTP of section D--E isienergized. This closes a front contact corresponding tofront. contact 3d of relay FTP with the result the repeater relay TPD is operated to bring about the control of relay DH, condenser 94 acting as a secondary source of energy in the control of relay DH. Approach relay ARD and its repeater relay APD at location D will be deenergized due to the shunting of the feed-back impulses by'this train entering the section next in the rear, and with relay APD released to close back contact 91 a charging circuit is completed for a condenser 95 through which feed-back current impulses are supplied to the rails of section. DE. This charging circuit for condenser 95 extends irom terminal B3 through front contact 96 of track relayDR3, condenser 95, back contact 91 of relay APD and front contact 98 of control relay DH to terminal N3. Condenser 95 is connected across the rails through back contact 99 of relay DB3 and is discharged to supply a feed-back current impulse. This feed-back current impulse is of a polarity to energize approach relay AR at location E which relay in Fig. 3 is connected across the rails through a rectifier I00 poled to block the current supplied by track battery BEI. Ree lay DB3 will not be energized by this feed-back current impulse due to rectifier 86. With approach relay AR operated by the feed-back current impulses, its associated repeater relays AP and APP are energized. With relay AP picked up to close front contact 30, the energizing circuit of repeater relay 'IPE and the charging circuit of condenser 81 are completed and control relay EH is energized in response to code operation of the track relay ER3. Control relay EH on picking up to close front contact 8'! connects battery BEI to the rails through code transmitter CTI80, so that the track circuit for section D-E is now supplied with current of the 180 code rate, withthe result that control relay DD is energized and signal SD is controlled as requiredto display a clear signal indication.

In the event a second train occupies the section next in advance of section D--E, the shunting of track relay EH3 causes oontrolrelay EH to be released so that the track. circuit current for section D--E is of. the code rate, with the resultcontrol relay DH is picked up but control relay DD is released and signal SD is controlled as required to display an approach signal indication. I

' When the train advances and enters section DE, the shunting of the rails causes an increase in the track circuit current and the second armature of either codetransmitter C'Il5 or CTI is picked up with the result the approach relay FTP is energized to close front contact 3|. The feed-backrcurrent impulses for the section DE are now shunted so that approach relay AR and its repeater relay AP are deenergized. Control relay EH remains energized because the connection for repeater relay TPE and condenser 8! is now closed at front contact 31 of relay FTP. With relay AP released and relay EH picked up, a charging circuit for a condenser l03 is formed from terminal B3, front contact [B8 of relay EH3, condenser I93, back contact I9! of relay AP and front contact I02 of relay EH to terminal N3. then discharged through back contact 10! of track relay ER3 for supplying a. feed-back current impulse to the rails of the section next in advance. With back contact 61 of relay AP and front contact 58' of relay FTP closed, the operating circuits for signal SE are completed andthe clear or approach lamp of the signal is illuminated according to the condition of control relays EH and ED.

The apparatus here disclosed has the advantage that a single battery only is: required for each track circuit supplied with coded direct current, different traffic conditions being reflected by'the' polarity and coderate of the current. Also approach control apparatus cooperating with Condenser I 03 is ed claims without departing from such track circuit is effective to provide approach control for two sections in advance of a train.

Althou h I have herein shown and described only three forms of apparatus for railway signal systems embodying my invention, it is understood that various change-s and modifications may be made therein within the scope of the appendthe spirit and scope of my invention.

Having thus described my invention, what I claims is: V

1. In combination with a railway track circuit including the rails of a section and a track relay connected across the rails at one end of said section, a source of direct current, a code transmitter having a first contact memberbiased to a first position where it engages a fixed contact and operable to a second position where it is out of engagement with said fixed contact when a winding of the transmitter is energized, circuit means including said fixed contact and said contact member to connect said current source across the rails at the end of said section opposite said one end through said winding to code the current supplied to said track circuit for operating said track relay at said code when the section is unoccupied, a second contact member operable by said transmitter to engage a fixed contact only when said transmitter winding is energized at a relatively high value of current to close' the last mentioned contact only when a train occupies the section to shunt the rails, and

14 a first and a second signaling means controlled by said track relay and said second transmitter contact member respectively.

2. In combination with a railway track circuit including the rails of a track section and a track relay connected across the rails at one end of the section and a track battery connected across the rails at the other end of the section, a code transmitter having a first contact member biased to a first position and operable to a second position when its Winding is energized, said contact member at its first position and said winding in series interposed in the connection of said track battery to code the track circuit current for code operating said track relay when the section is unoccupied, a second contact member for said code transmitter and which second contact member is biased to a first position and is operated to a second position only when the transmitter is energized at a relatively high value of current to close a front contact when a train occupies said section to shunt the rails, supply means controlled by said track relay when code operated to supply to the rails an impulse of current each code period the track relay is de energized, a first signaling means including said first contact member at its second position energized by said current impulses when the section is unoccupied, and a second signaling means including said front contact and a current source energized when a train occupies the section.

FREDERICK T. FEREDAY. 

